1. Field of the Invention
The present invention relates to a multi-functioned wafer aligner, and more particularly, to a multi-functioned wafer aligner performing a wafer centering compensation, a wafer flat zone alignment, and a wafer breakage or damage detection.
2. Description of Related Art
Recently, rapid developments in the field of semiconductor devices has produced highly integrated and highly efficient storage devices capable of storing enormous quantities of data for processing in short periods of time. Such semiconductor devices are broadly employed in various fields of the information processing industry, computer industry, telecommunication industry, aerospace industry, among many others.
Fabricating such semiconductor devices necessarily includes processes for manufacturing a pure silicon wafer, fabricating multiple semiconductor chips, packaging the chips, and then testing them.
The process of fabricating multiple chips involves a series of very accurate multiple semiconductor fabrication processes, such as for example, a thin film growing/depositing process, an etching process, an ion implanting process, and so forth. The thin film growing/depositing process produces various kinds of thin films with predetermined characteristics on a wafer, the etching process selectively removes a portion of the thin films, and the ion implanting process injects impurities forcedly to improve a thin film or wafer characteristic.
The above-described semiconductor chip fabrication process simultaneously produces multiple semiconductor chips in a wafer of a predetermined diameter to maximize productivity and to improve yields. To produce multiple semiconductor chips simultaneously in a wafer through multiple fabrication processes, the wafer should be always located on and processed in a fixed position of the corresponding equipment to the corresponding process.
To satisfy such requirements, a portion of the wafer sliced from a cylindrical ingot is cut off and a flat zone for recognizing a position of the wafer is generated on the wafer as a result. It is then necessary to adjust the position of the wafer accurately in aligning the flat zone and center the wafer before the wafer is put into the corresponding semiconductor processing equipment. Equipment designed to perform this alignment are normally called a “wafer aligners.”
In a typical wafer aligning process, wafers in a lot unit are loaded into a wafer cassette. A wafer transfer arm unloads a wafer from the wafer cassette and transfers it to a rotation chuck, whereupon the wafer is rotated at a predetermined speed by the rotation chuck. A sensor beside the rotation chuck recognizes any eccentric displacement of the wafer, and the wafer transfer arm adjusts the wafer position to center the wafer and eliminate the eccentricity. After centering the wafer, the rotation chuck is rotated to perform a flat zone alignment to the wafer, wherein a sensor detects the flat zone and halts the rotation of the chuck. The wafer transfer arm transfers the wafer from the rotation chuck back to the wafer cassette. After all the wafers have been centered and aligned, the cassette is transferred into the semiconductor fabricating equipment for the next process.
In some systems, after completion of the centering and a flat zone alignment, the wafer is transferred to the semiconductor device fabricating equipment, wherein it is loaded onto a wafer chuck in the equipment and a process performed to the wafer. After the equipment completes the process, the wafer is unloaded from the wafer chuck of the equipment. However, wafer breakage occurs too frequently in this process.
A wafer may break for various reasons. The main reason is that the wafer gets a small crack or a breakage in the wafer edge during a previous manufacturing step. In this case, when stress is overly focused on the crack or the breakage in the wafer edge, the wafer can fatally break during subsequent processing steps, rendering the wafer useless.
Therefore, to prevent such an eventual breakage of the wafer, there is needed a means to inspect and detect the crack or the breakage in the wafer edge before transferring the wafer to the next semiconductor device fabricating step.